Thursday, April 30, 2009

Lecture 28

Today we talked about barriers to proving PNP and other complexity-theory results: specifically, the "relativization" barrier introduced by Baker-Gill-Solovay, and the "natural proofs" barrier introduced by Razborov-Rudich.

We also talked about results that evade them. For example, the Hopcroft-Paul-Valiant Theorem, TIME[f(n)]SPACE[f(n)], and the Paul-Pippenger-Szemeredi-Trotter Theorem, DTIME[n]NTIME[n], do not relativize. Nor do they algebrize, according to the Aaronson-Wigderson notion. (At least, my opinion is that the notion of relativizing/algebrizing makes sense for these theorems, and in this sense they do not relativ/algebrize.)

As for natural proofs, we discussed how proofs by diagonalization do not seem to naturalize, and we mentioned explicit circuit lower bound which are by diagonalization; for example, Kannan's result that Σ4 not in SIZE(n1000).

Finally, we mentioned some theorems that neither relativize nor (seem to) naturalize: for example, Vinodchandran's Theorem that PP not in SIZE(n1000), and Santhanam's improvement of this to an explicit promise problem in MA which isn't in SIZE(n1000).

2 comments:

  1. Are there any notes that could be posted? (I had to leave for a thesis defense.)

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  2. My notes for this aren't so polished; I'll email them to you.

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